1. Field of the Invention
This invention relates to a signal processing method for analyzing an autoradiograph.
2. Description of Prior Art
It is known that autoradiography can be used as a method for obtaining locational information on radioactively labeled substances distributed at least in one-dimensional direction on a support medium.
For instance, there is known an autoradiography comprising steps of: labeling organism-originating biopolymers such as proteins and nucleic acids with a radioactive element; resolving the mixture of the radioactively labeled biopolymers, derivatives thereof, cleavage products or synthetic products thereof on a gel support (medium) through a resolving process such as gel electrophoresis; placing the gel support medium and a high-sensitivity X-ray film together in layers for a certain period of time to expose said film to the gel support, and then performing the isolation and identification of the polymeric substances, determination of molecular weight of the polymeric substances and evaluation of characteristics of the polymeric substances based on the obtained locational information of the radioactively labeled substances from the exposed part of the film.
Recently, the autoradiography has been effectively used especially for determining the base sequence of nucleic acids such as DNA and RNA. Further, the autoradiography is an essential means for the screening of genes using a hybridization process such as Southern blotting, Northern blotting or colony hybridization.
For the purpose of simply carrying out the determination of the base sequence of nucleic acids with high accuracy in said autoradiography, there are described in co-pending U.S. patent application Nos. 664,405 (now abandoned) and 837,037 (now abandoned) autoradiographic procedures which utilize a radiation image recording and reproducing method using a stimulable phosphor sheet in place of the above-mentioned conventional radiography using a radiosensitive material. The stimulable phosphor sheet comprises a stimulable phosphor and has such properties that when exposed to a radiation, the stimulable phosphor absorbs a portion of radiation energy and then emits light (stimulated emission) corresponding to the radiation energy stored therein upon excitation with an electromagnetic wave (stimulating rays) such as visible light or infrared rays. According to this method, exposure time can be greatly shortened and there is no trouble of causing problems such as chemical fog associated with prior arts. Further, since the autoradiograph having information on radioactively labeled substances is stored in the phosphor sheet as radiation energy and then read out as stimulated emission in time sequence, information can be expressed by the form of numerals and/or symbols in addition to an image.
The analysis of an autoradiograph has been conventionally made by visually judging each of the resolved portions (bands) of the radioactively labeled substances on a visualized autoradiograph, thus obtaining locational information on the radioactively labeled specific substances (and identification of biopolymers, determination of molecular weight and evaluation of characteristics of biopolymers based on the obtained locational information of the radioactively labeled substances). For instance, the base sequence of the nucleic acids has been conventionally determined by visually comparing the positions of the bands of the mixture of the base-specific fragments of the nucleic acids such as DNA and RNA. Thus, the analysis of the autoradiograph requires great amounts of time and labor.
Further, since the visual analysis of the autoradiograph varies or fluctuates owing to the skill of investigators, the results on the determination of the base sequence of the nucleic acid vary depending on the investigators and the accuracy of information is limited to a certain extent.
In order to improve the accuracy of information, there are proposed in co-pending U.S. patent application Nos. 568,877 (now abandoned), 730,034 (now abandoned) 917,606 and 917,609 methods for automatically obtaining locational information on the radioactively labeled substances in the form of numerals and/or symbols by obtaining the autoradiograph as digital signals and subjecting the digital signals corresponding to the autoradiograph can be obtained either by visualizing the autoradiograph on a radiographic film and photoelectrically reading out the visible image on said film by means of reflected light or transmitted light when the conventional radiography is used, or by directly reading out the stimulable phosphor sheet without the visualization of the autoradiograph when the radiation image recording and reproducing method is used.
However, the resolved pattern obtained by resolving (developing) radioactively labeled substances on a support medium by electrophoresis or the like is liable to cause various distortion and noise.
For instance, when the autoradiograph of the resolved pattern obtained by electrophoresing base-specific DNA fragments to determine the base sequence of DNA is illustrated in the form of a kind of a bird's-eye view (a view obtained by superposing a number of waveforms composed of a position and a signal level along the developing direction), there can be obtained FIG. 2 wherein background noise is very large and the positions of intrinsic bands can be scarcely determined. FIG. 2 is such a bird's-eye view showing the autoradiograph of the resolved pattern, wherein the developing direction is in the y-direction.
The background noise is produced, when a sample is contaminated with radioactive impurities by poor labeling of the base-specific DNA fragments with a radioactive element in the course of the preparation of the sample, or when a stimulable phosphor sheet or a radiosensitive material is exposed to a natural radiation.
Accordingly, it is desirable to provide an image suitable for analysis by simply eliminating such noise in the cases of the automatic analysis of the autoradiograph by digital signal processing as well as the analysis of the autoradiograph by visually judging the visualized image.